> Those are individual countries doing great

These countries are doing great because they are part of the EU. If anyone disagrees, well, it's not like we lack experimental data:

https://www.london.gov.uk/new-report-reveals-uk-economy-almo....

https://www.gisreportsonline.com/r/brexit/

https://www.politico.eu/article/political-gridlock-northern-...